The general objective of this work is to develop an easily used electromagnetic applicator that will heat deep lying tumors during hyperthermic procedures. The specific aims are: 1) Design an optimized H-type hyperthermia applicator based on computer modelling using the Finite Difference Time Domain Technique and 2) Test the prototype applicator on a phantom model of the human thorax. Optimization of the electromagnetic applicator design will be accomplished by the use of a three dimensional finite difference time domain (3 FDTD) computer program that we have previously developed. This powerful technique calculates heating patterns for applicators without assuming aperture field distributions, thus allowing optimization of performance by variation of applicator configuration. Preliminary experimental data on a 27 MHz magnetic induction applicator in an inhomogeneous phantom gives half power heating at a depth of 5 cm. Because of its promise this applicator will be the first one studied. Since the FDTD is flexible and provides accurate results in a short time other types of applicators will also be studied.